The present invention is related to a newly discovered human chorionic gonadotropin releasing factor (hCG-RF) and its uses such as affecting states of pregnancy.
Gonadotropin releasing hormone-like material has been identified in various biological fluids or tissues such as hypothalami, semen, testes, placenta, pancreas or mammary . carcinoma, for example. It is generally believed that gonadotropin releasing hormone (GnRH) is identical or similar to luteinizing hormone releasing factor (LRF) and is a small peptide. This small peptide is generally agreed to be a decapeptide with the amino acid sequence: pyro-glu-his-trp-ser-tyr-gly-leu-arg-pro-gly-NH.sub.2. Gn-RH-like material appears to be synthesized by placenta and numerous other tissues as well as to have receptor sites in diverse organs. The present invention describes a human chorionic gonadotropin releasing factor (hCG-RF) which has never before been identified and is completely unique in many ways from GnRH. Antibodies directed toward GnRH have indicated the presence of GnRH-like material at numerous other biological sites. A 92 amino acid peptide has been reported which contains the decapeptide GnRH (Seeburg et al., Nature (1984) V. 311, p. 666), but the human chorionic gonadotropin releasing factor (hCG-RF) described herein differs from it.
Earlier studies have demonstrated that an immunologically and biologically active GnRH was synthesized and released from human placental extracts. This GnRH eluted from CM-cellulose in the same area as synthetic GnRH. In addition, Lee at al. (Acta Endocrinol. (1981) V 96 p 394) reported a apparent GnRH immuno-activity from acid extracts of placentas that eluted on HPLC in the area of GnRH. These findings led to the hypothesis that placental apparent GnRH immuno-activity and synthetic GnRH were chemically similar. Additionally Tan et al. (Biochem Biophys. Res. Commun. (1982) V 109 p 1061) reported that the GnRH decapeptide sequence was present in the acid extracts of placenta. More recently, Seeburg et al (Nature (1984) V 311 p 666), using cDNA expression, have deciphered an mRNA coding for 92 amino acids in which the GnRH sequence is contained.
Certainly, the presence of the decapeptide GnRH in the placenta has been firmly supported. The role of GnRH in placental endocrinology has not been answered by the above cited studies. It has been demonstrated that synthetic GnRH can affect placental hormonogenesis, yet high concentrations are needed. An antagonist of GnRH has been shown to inhibit placental hormonogenesis both in vitro (Siler-Khodr et al, Life Sci. (1983) V. 32, p. 2742 and Siler-Khodr et al., Fertil-Steril (1984) V 41 p 448) and in vivo. Other studies have demonstrated that a placental receptor recognizes synthetic GnRH; however, the dissociation constant of the placental receptor for synthetic GnRH was found to be only 10.sup.-7 M and a potent antagonist of GnRH on the pituitary had no greater affinity for this placental receptor than did GnRH. Thus, it appeared that the placental receptor recognizing synthetic GnRH differed from the pituitary receptor. The inventors have also noted that, although there was newly synthesized apparent GnRH immuno-activity recovered in the GnRH area following CM cellulose chromatography, it accounted for &lt;1% of the apparent GnRH immuno-activity. In addition as reported herein, it was observed that apparent GnRH immuno-activity of the placenta was extracted with a very low yield with methods typically utilized for extraction of hypothalamic GnRH, i.e. acid or methanol. These findings led the inventors to consider the possibility of there being more than one substance effecting this activity in the human placenta.